The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device, and in particular, to a semiconductor device having a vertical transistor and a method of manufacturing the semiconductor device.
One of semiconductor devices includes a semiconductor device having a vertical transistor. The vertical transistor is, for example, used for an element that controls a high current. Some vertical transistors have a trench gate structure. A transistor with the trench gate structure has the following structure. First, a concave portion is formed in a substrate. A gate insulating film is formed on a side surface of the concave portion. Additionally, a gate electrode is buried in the concave portion.
One of the characteristics required for the transistor with the trench gate structure includes lowering an on-resistance and raising a drain withstand voltage. The on-resistance and the drain withstand voltage are generally conflicting characteristics. In contrast to this, a transistor described in FIGS. 11 and 12 in Patent Document 1 (Japanese Patent Laid-Open No. 2009-302436) has an n-type current dispersion layer between an n-type drift layer and a p-type channel layer (base layer) in order to lower an on-resistance while raising a drain withstand voltage. In this technology, the current dispersion layer is located above an insulating film of a bottom of a concave portion.
In addition, Patent Document 2 (Japanese Patent Laid-Open No. 2008-277352) describes that an n-type well layer is formed between a p-type body layer (corresponding to a channel layer) and an N-layer (corresponding to a drift layer). When viewed in a thickness direction of a substrate, an upper end of the well layer is located above an insulating film of a bottom of a concave portion, and a lower end of the well layer is located below the insulating film of the bottom of the concave portion.